Marshall–Smith syndrome (MSS) and Malan syndrome (MS) are both allelic disorders caused by mutations in the NFIX gene. MS is characterized by overgrowth, intellectual disability, distinctive facial features, and accelerated skeletal maturation. On the other hand, clinical features of MSS consist of advanced bone age, dysmorphic features, intellectual disability, and failure to thrive at birth. In this study, we presented the clinical and molecular findings of two different patients with MS and MSS as a rare cause of intellectual disability and reported two novel variants in the NFIX gene. NFIX gene sequencing revealed a novel heterozygous c.1287delC (p.G430Vfs*34) mutation in patient 1 whose clinical diagnosis was compatible with Marshall–Smith syndrome, and in the second patient, physical features consistent with Malan syndrome, was detected a heterozygous one nucleotide duplication, c.303dupC (pCys102LeufsTer17).

中文翻译：

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智力障碍的罕见原因：两名具有马歇尔-史密斯综合征和马兰综合征临床特征的患者的 NFIX 基因新突变

马歇尔-史密斯综合征 (MSS) 和马兰综合征 (MS) 都是由NFIX基因突变引起的等位基因疾病。MS 的特点是过度生长、智力障碍、独特的面部特征和骨骼成熟加速。另一方面，MSS 的临床特征包括骨龄提前、畸形特征、智力障碍和出生时发育不良。在这项研究中，我们介绍了两名不同的 MS 和 MSS 患者的临床和分子发现，MSS 是智力障碍的罕见原因，并报告了NFIX基因的两种新变异。NFIX基因测序显示，临床诊断符合马歇尔-史密斯综合征的患者 1 存在一种新的杂合 c.1287delC (p.G430Vfs*34) 突变，而第二名患者的身体特征与马兰综合征一致，检测到杂合突变核苷酸重复，c.303dupC (pCys102LeufsTer17)。